1. Field of the Invention
The invention relates to a process and apparatus for the removal of interfering materials from an aqueous fiber pulp suspension.
2. Discussion of Background Information
Processes of the aforementioned type are used in order to remove at least a portion of the interfering pulp particles suspended in a fibrous pulp suspension containing fiber pulp. It is common knowledge that a foam or floating slurry, containing the material to be removed, is created in a flotation process. A typical case of application of such a process is the processing of aqueous fibrous pulp suspensions that are produced from printed used paper, whereby the ink is already dissolved from the fibers so that it can be floated out. The flotation process described here utilizes the differences between the fibrous pulp and the undesirable solid particles such that the fibrous pulp, due to its hydrophilic nature remains in the fibrous pulp suspension, while the described solid particles exhibit hydrophobic behavior and therefore end up with the air bubbles in the foam. Aside from the ink particles there are also a large number of additional materials that are hydrophobic and are able to be separated from the fibrous pulp by flotation. Such materials are in particular adhesives, fine synthetic material particles, and possibly also resins. When the fibers are to be separated from contamination, i.e. not all solid particles are to be sorted out, a selective flotation process is performed. The term "flotation de-inking", also used, is generally not only used for the removal process of ink particles, but also used in a more general sense for the selective flotation of contamination of fibrous pulp suspensions.
The state of the art in regards to flotation processes for fibrous pulp suspensions is already at a very advanced state. There are thus solutions which are quite suitable in removing a large portion of the solid particles by flotation. However, the effect weakens when the amount of fibers in the suspension is relatively high, for example 2%, instead of the conventional amount of around or below 1%. In such cases problems often occur since the resistance for the gas bubbles is already high with a higher fiber content, thereby making it difficult to separate the suspension. Higher pulp densities, on the other hand, are desirable in order achieve a higher throughput.